In
the shaft at the beginning of AotCR, you can only fly so far down before the
game stops the vehicle from moving any further. If you ride the pelican
down, you will eventually die. So how do you get past the
boundary? ...

If
you get into the banshee at the lower level, the game will shoot you back up
to the next level. There are more ledges down below, and past that the
bottom might not be too far away. Can it be reached?